Faster than electron speed: photodetectors with confined 2D charge plasma overcome transit-time limit

High-speed photodetectors’ intrinsic response is limited by the transit time of the carriers that light generates to the contacts that collect these carriers generating an electric response in the external circuitry. By contrast, charge plasma confined in a semiconductor can transfer energy, hence responding much faster, than the field-induced carrier drifts current. The analogy is to a drop exciting a wave in a reservoir, which is detected more rapidly than the drop’s transport by current flow. Here we construct a photodetector device in which charge reservoirs of confined two-dimensional electron and hole gasses (2DEG, 2DHG) mediate the photodetector response circumventing charge transport limitations in both expended energy and required velocity. In response to short optical pulses, this device produces electrical pulses which are almost two orders of magnitude shorter than the same device without the charge reservoirs. In addition to speed, the sensitivity of this process allows us to measure, at room temperature, as low as 11,000 photons. The device is shown to operate without applied bias, with high responsivity, at hundreds of gigahertz. These microplasma devices can have a range of applications such as optical communication with a fraction of a microwatt power compared to the present tens of milliwatts, ultrasensitive detection of light without the need for cryogenic cooling, photovoltaic devices that are capable of harvesting dim light, detectors of THz radiation, and in the detection of charged particles.